The present invention relates to a device for verifying the operational conditions of a monitor, designed to distinguish easily between a computer malfunction and a monitor malfunction by removing the signal cable of the monitor from a computer to which it is connected, in the event that the computer system gets out of order. In general, when a computer system error occurs, it is possible to distinguish between a computer malfunction and a monitor malfunction by applying a direct current voltage to the video signal input terminal of the monitor used in connection with the computer.
The conventional device for verifying the operational conditions of a monitor, as shown in FIG. 1, is formed, by way of example, by connecting the base of a transistor TR1 connected with a video signal imput terminal Vi to a power supply terminal B.sup.+ through a switch SW1 and a resistance R2. According to this conventional device, therefore, in the event that a display corresponding to the output of the computer is not shown on the monitor, the operational conditions of the monitor are verified by short-circuiting the switch SW1 mounted in an interior of the monitor and applying the electric potential source of the power supply terminal B.sup.+ to the base of transistor TR1 through the resistance R2 and switch SW1 so as to put out a low-potential signal, the video signal output terminal Vo of which is the collector of the transistor TR1. Therefore, if no abnormality exists in the deflection circuit, power supply circuit and video circuit, bright video signals are shown on the Braun tube of the monitor by the low-potential signals appearing on the said video signal output terminal Vo, by which a normal condition of a monitor is verified and the computer malfunction is determined. On the contrary, if bright video signals are not shown on the Braun tube of the monitor, a monitor malfunction is diagnosed.
However, with such a conventional device, when the computer system gets out of order, the switch mounted in the interior of the monitor is short-circuited only after disassembling the housing of the monitor in order to verify its operational conditions.